This invention relates to a method for the permanent waving of hair by reductive cleavage and oxidative reformation of disulfide bonds of the hair keratin, in which the waving effect is enhanced by aftertreatment with a novel composition containing an aluminum (III) salt and a C.sub.4-6 hydroxydi- or tri-carboxylic acid. 2. Statement of Related Art
In known permanent waving methods, the permanent shaping of hair is achieved by mechanically shaping the hair and fixing the applied shape, for example by winding onto hair curlers or rollers. Before and/or after this shaping step, the hair is treated with an aqueous preparation of a keratin-reducing substance, rinsed with water after a short contact time, and then treated in a second step with an aqueous preparation of an oxidizing agent. After a suitable contact time, the oxidizing agent is also rinsed out of the hair and the mechanical shaping aids (curlers, rollers) removed from the hair.
The aqueous preparation of the keratin reducing agent is normally alkalized to a considerable degree in order to swell the hair, thus enabling the keratin-reducing substance to penetrate deeply into the hair. The keratin-reducing substance cleaves some of the disulfide bonds of the keratin to --SH groups, so that the peptide network is loosened and the keratin structure is reoriented under the strain applied to the hair by the mechanical shaping treatment. Under the influence of the oxidizing agent, disulfide bonds are reformed and the keratin structure is thus refixed in the predetermined shape.
Neither the swelling effect of the alkali nor the keratin-splitting effect of the reducing agent can be completely neutralized, so that freshly permanently waved hair is extremely sensitive to mechanical stressing. Excessive reduction, for example through an excessive concentration of keratin-reducing substance or an overly long contact time, can also lead to severe hair damage, resulting in cosmetically undesirable overcurling of the hair.
It would be extremely desirable to provide a process for the permanent shaping of hair, in which the risk of unwanted side effects is avoided with greater certainty and in which the hair is less heavily stressed. Such a possibility would exist if it were possible to reduce the concentration of the keratin-reducing substance in the reduction step and to enhance shaping of the hair by less hair-damaging measures.
According to U.S. Pat. No. 3,266,994, a water-soluble magnesium, aluminium or calcium salt is added to the oxidative fixing solution. U.S. Pat. No. 3,981,312 describes a process for the permanent shaping of hair in which the hair is treated between the reduction step and the oxidative fixing step with a setting solution containing a polyvalent metal salt in aqueous solution. Finally, U.S. Pat. No. 4,409,204 describes an aftertreatment preparation for permanently waved hair which contains glyoxylic acid and certain unsaturated carboxylic acids. These measures were intended in themselves to counteract the loss of strength of the hair as a result of the permanent waving treatment. However, no satisfactory improvement was achieved through the measures mentioned.